1. Field of the Invention
The invention relates to a motorcycle comprising a belt type continuously variable transmission.
2. Description of Related Art
A motorcycle comprising a belt type continuously variable transmission (CVT) is known (refer to JP-B-61-40864 and JP-B-6-57547, for example). The CVT comprises a V-belt wound around a primary and a secondary sheave. Heat is generated due to friction between the V-belt and the sheaves in operation of the CVT. Accordingly, it is preferable to provide an intake path to supply the CVT with air for cooling.
JP-B-61-40864 discloses a power unit comprising a two cycle type engine, a CVT and an intake path for cooling the transmission at a position lower than an upper end of a crank case of the engine. JP-B-6-57547 discloses a power unit comprising a two cycle type engine, a CVT and an intake path for cooling the transmission extending to a position higher than the crank case.
Providing a CVT on an off-road vehicle would be advantageous since it would make the troublesome clutch operation unnecessary. However, because there are problems in applying the structures of JP-B-61-40864 and JP-B-6-57547 to off-road vehicles, a CVT including an intake path for cooling has not yet been applied to an off-road vehicle.
When an intake path is provided at a position lower than the upper end of the crank case, as in JP-B-61-40864, water and dust can easily rise from the ground to enter into the intake path. Therefore, the structure of JP-B-61-40864 is problematic for off-road vehicles that often run on unpaved roads and the like.
Further, in an off-road vehicle, a cylinder of the engine rises up and an angle between the cylinder and a horizontal line is large. Moreover, because the minimum height of a power unit from the ground should be comparatively high, the cylinder and exhaust pipe are provided above the crank case. The exhaust pipe and cylinder are thereby obstructive to extending the intake path to a position higher than the crank case, as in JP-B-6-57547.
For these reasons, it has been difficult to mount a CVT with an air intake path to an off-road vehicle or motorcycle using conventional technology.